Inkjet printing apparatuses are used for single- or multicolor printing of a printing substrate, for example of a single sheet or a belt-shaped recording material made of the most varied materials (paper, for example). The design of such inkjet printing apparatuses is known—see for example EP 0 788 882 B1. Inkjet printing apparatuses that operate according to the drop-on-demand (DoD) principle, for example, have as a printing unit a print head or multiple print heads with nozzles comprising ink channels (whose activators, controlled by a print controller, excite ink droplets in the direction of the printing substrate). These nozzles are directed towards the printing substrate in order to apply print dots for a print image there. The activators can generate ink droplets thermally (bubble jet) or piezoelectrically.
DE 197 26 642 C1 describes a device for positioning an inkjet print head and a cleaning and sealing device. The inkjet print head can be pivoted from a printing position into a cleaning position and back again. A cleaning and sealing device can be displaced onto the inkjet print head and away from the head again. The cleaning and sealing device has a sealing cap and a wiping lip.
In an inkjet printing system, the print heads of one color are mechanically attached on a print bar. In the printing operation, different spacings of the nozzles of the print heads relative to the printing substrate are necessary for cleaning and maintenance. For this the print bar (and therefore the print heads) must be able to be moved in the vertical direction to different positions at different distances from the printing substrate. It must be possible to set two of these positions:                The printing position: positioning of the print heads parallel to the printing substrate; for this the print bar must be able to be adjusted to a height, tilted or set at an angle relative to the printing substrate, and translationally transverse to the travel direction of the printing substrate.        Cleaning position: position for cleaning the nozzles of the print heads. For example, in the cleaning ink is pushed or sucked through the nozzles of the print heads via overpressure or negative pressure. This ink is then subsequently stripped with a rubber lip or multiple rubber lips (called wiping). For this the print bar can be driven over the rubber lips or the rubber lips can be driven over the print bar. An exact positioning of the print bar relative to the rubber lips is necessary in order to ensure a constant overlap between the rubber lips and the nozzles.        
From U.S. Pat. No. 6,095,701 it is known to bear a print head in a print head receptacle so that it can be adjusted in three directions. It is thereby possible to adjust the print head at the installation site.
U.S. Pat. No. 7,090,329 B2 describes a printing unit in which the print heads are arranged on rods. The print heads can be displaced on the rods; in addition to this the rods can be rotated with the print heads.
DE 100 57 062 C1 describes a method according to which print heads can be aligned relative to a print good. In addition to this, the print heads can be moved relative to one another, transverse to the printing direction. The print image can hereby be adjusted transverse to the printing direction.
DE 693 01 763 T2 discloses an inkjet printing apparatus in which the print heads are arranged on sliding means so that the print heads can be moved parallel and perpendicular to the direction of the print medium. The print heads can thereby be arranged offset from one another or with the ends at one another.